This invention relates to techniques for restoring subterranean formations which have been subjected to oxidative in situ leaching of uranium values.
Recovery of uranium values from subterranean formations involves in the usual methods the oxidation of insoluble tetravalent uranium into soluble uranyl complexes that may be drawn from the formation by leaching. The overall reaction in oxidative in situ leaching may be described as follows: EQU UO.sub.2 (S)+[O]3HCO.sub.3.sup.- .fwdarw.UO.sub.2 (CO.sub.3).sub.3.sup.-4 +H.sup.+ +H.sub.2 O
The use of oxygen, however, also solubilizes insoluble molybdenite into the toxic soluble molybdate ion: EQU MoS.sub.2 +9[O]+3H.sub.2 O.fwdarw.MoO.sub.4.sup..dbd. +6H.sup.+ +2SO.sub.4.sup..dbd.
Current environmental regulations restrict the amount of molybdenum permissible in formations after leaching to less than one ppm in New Mexico, for example.